1 Spinoza on the Unity of Will and Intellect

While Aristotelians debated about whether the parts of the human soul are really distinct or not, they all agreed that there are three types or kinds of souls: first, there is the vegetative soul that is responsible for a living being’s metabolism and reproduction, second, there is the sensitive soul that accounts for the perceptions and movements of animals, and third the rational soul enables rational beings to think and to perform actions. It was this shared assumption that Descartes rejected by way of arguing for substantial dualism. According to Descartes the human soul (or as he preferred to say: the human mind)1 only consists in the rational soul that accounts for our intentional actions and ability to think. The two other and lower kinds of Aristotelian souls –namely the vegetative and the sensitive soul – he relegated to the res extensa by arguing that all bodily functions they were supposed to explain, may be explained more perspicuously by appeal to simple causal mechanisms governed by the laws of motion. So, in contrast to the Aristotelians who accepted three kinds of souls, Descartes was a convinced monist concerning types of souls: There is only one kind of souls, namely the res cogitans or the mind.2 However, Descartes was no monist concerning the kinds of acts the immaterial min